The problem of power factor in VRPM (transverse-flux) machines

The purpose of the paper is to explore the theory of power factor in variable reluctance permanent magnet (VRPM) machines and to understand what physical features of these machines tend to cause the low value. A single figure of merit, for a given design, is identified that effectively determines what the best available working power factor may be. The same figure of merit is applicable to synchronous machines of conventional configuration, so that comparison can be made between VRPM and conventional machines and the fundamental reasons for their difference in working power factor understood. The scope for power factor improvement in VRPM machines can then be examined, by changing the electromagnetic design so as to modify the figure of merit appropriately. However, it will become clear that a very limited amount of improvement is possible, and low working power factor seems to be the price that must be paid for the high specific output.